I am in the process of writing a scanner that scans an assembly
language that was written for a specific processor. This language is
very old, and the current assembler has some issues that need to be
reworked.

I am having trouble figuring out how to scan for comments in the file.
A comment can start with a star, which is easy enough, "*"[^\n]*

But text in the fourth column of the file is also considered a
comment. And this type of comment does not start with any kind of
special character like the '*'. Here is an example:

label Operator op1,op2 Comment

So I am really confused about how to throw away this type of comment
for the yacc parser. How can I write a regular expression to catch a
comment that is not associated with a '*' or something.
[Basically, you can't. I suspect you can use start states and some
whitespace counting hackery to switch into a state after the operands
that swallows up the rest of the line. -John]